Cryo-Electron Microscopy Structure of a Yeast Mitochondrial Preprotein Translocase

The translocase of the outer mitochondrial membrane (TOM) complex is the main entry gate for proteins imported into mitochondria. We determined the structure of the native, unstained similar to 550-kDa core-Tom20 complex from Saccharomyces cerevisiae by cryo-electron microscopy at 18-angstrom resolution. The complex is triangular, measuring 145 angstrom on edge, and has near-3-fold symmetry. Its bulk is made up of three globular similar to 50-angstrom domains. Three elliptical pores on the c-face merge into one central similar to 70-angstrom cavity with a cage-like assembly on the opposite t-face. Nitrilotriacetic acid-gold labeling indicates that three Tom22 subunits in the TOM complex are located at the perimeter of the complex near the interface of the globular domains. We assign Tom22, which controls complex assembly, to three peripheral protrusions on the c-face, while the Tom20 subunit is tentatively assigned to the central protrusion on this surface. Based on our three-dimensional map, we propose a model of transient interactions and functional dynamics of the TOM assembly. (c) 2008 Elsevier Ltd. All rights reserved.